Buenas tardes,
Please visit this link:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/rel_notes/5_1_3/513cmrn.html
Search the document for the sentence "Recovering Administrator and Security Passwords".
This section is close to the end of the document. You will find what you're looking for there.
Please be careful! From the text: "The security password on all nodes in a cluster must match. Change the security password on all machines, or the cluster nodes will not communicate."
I hope that helps you!
Regards,
-James.